Norovirus causes up to 21 million cases of acute gastroenteritis and about 800 deaths annually in the United States. Older adults in long-term care (LTC) facilities are particularly at risk. The Pennsylvania Patient Safety Authority analyzed norovirus cases reported by LTC facilities during the three most recent norovirus seasons. Reports to the Authority showed that norovirus events comprised more than 40% of all gastrointestinal infections. The norovirus outbreak rate varied by region within the state, but with the exception of the Northcentral region in academic year 2016, all regions reported infections in each of the three years studied. In the timeframe analyzed, Pennsylvania LTC facilities reported an increased number of norovirus events from November through March—the typical norovirus season. This shows that norovirus infection control continues to be problematic in Pennsylvania LTC facilities, indicating a need to implement improved prevention and control strategies.
According to the Centers for Disease Control and Prevention (CDC), norovirus causes up to 21 million cases of acute gastroenteritis and results in about 800 deaths annually in the United States. Older adults in long-term care (LTC) facilities are particularly at risk. In a recent study, CDC found that among nursing home patients in three states, hospitalization and death rates increased by 10% during norovirus outbreaks. Also, the risk for hospitalization and death among patients 90 years of age or older increased by 20% to 30% during norovirus outbreaks.1,2
In LTC settings, most outbreaks are caused by person-to-person transmission, because of the high levels of personal contact in close spaces. Also, the hygiene of some residents, such as those who are physically or mentally impaired, may be inadequate.3 From an administrative viewpoint, norovirus outbreaks in healthcare facilities often result in significant financial and operational burdens.4 In 2010, the Pennsylvania Patient Safety Authority published an article about controlling the annual threat of norovirus gastroenteritis outbreaks, accompanied by a toolkit.4 Available data was limited at the time because norovirus infection was not reported in Pennsylvania as a distinct subcategory of gastrointestinal (GI) infections.
In April 2014, in accord with changes to national standards,5 the Authority revised the LTC criteria for identifying and reporting gastroenteritis. The revision included a new gastroenteritis subcategory that allows detailed surveillance and reporting of norovirus cases separate from other causes of gastroenteritis within the Pennsylvania Patient Safety Reporting System (PA-PSRS).
This first report since the standards were revised takes a fresh look at the incidence of norovirus gastroenteritis in Pennsylvania LTC facilities. The new criterion allows analysis of the number of cases and outbreaks of norovirus as a subset of overall GI infections.
Authority analysts queried the PA-PSRS database for GI infection reports for the three most recent academic years (AYs), AY2015 through AY2017 (July 2014 through June 2017). Analysts compared the proportion of norovirus events to other causes of GI infections by year and month, as reported to the Authority, and the number of outbreaks by year and month by regions (based on the Pennsylvania Department of Health's Public Health Districts).
A norovirus outbreak as defined by CDC is an occurrence of two or more similar illnesses characterized by staff and/or residents having vomiting and/or diarrhea within 48 hours, resulting from a common exposure that is either suspected or laboratory-confirmed to be caused by norovirus.6,7
Rates calculated for analytic comparisons used incidence per 1,000 resident days, as reported through PA-PSRS.
Of the 11,532 records of GI infections returned, 4,761 (41.3%) were categorized as norovirus events, compared with 6,682 (57.9%) classified as
Clostridium difficile infection, 81 (0.7%) classified as other bacteriologic GI pathogens, and 8 (0.1%) classified as
Pseudomembranous colitis. Figure 1 shows the percentages of types of infections over the three years. For two-thirds of the months analyzed in this time period,
C. difficile was the GI infection reported most often through PA-PSRS. However, norovirus events comprised the majority of GI infections for 12 of 36 months in three clusters of consecutive months concurrent with what is commonly considered the norovirus season (Figure 2). These three clusters accounted for 87.5% of all norovirus reports over the three-year period. Also of note are the seasonal spikes of monthly norovirus rates as compared to relatively stable monthly rates of other GI infections (Figure 3).
Events by Pennsylvania Region
The timing and magnitude of event clusters varied among facilities, as shown when grouped by Pennsylvania region (Figure 4). Each region had different monthly peaks, demonstrating that although events are seasonal, variability exists by region. Table 1 shows peak norovirus periods and rates for the Authority's six state regions.
Peak Month and AY||
Average Rate, AY15–AY17*|
Note: Academic years are for the 12 months ended June 30 of each year.
AY, Academic year.
* Rate calculated by number of norovirus reports per 1,000 resident days.
Of 222 LTC facilities reporting norovirus, 183 (82.4%) had norovirus clusters that met CDC's definition of an outbreak. These 364 outbreaks encompassed 4,564 (of 4,761, 95.9%) of the reported norovirus events in this period (Table 2). The longest outbreak was reported over the course of 27 days and included 138 cases. The most concentrated outbreak included 86 cases reported over two days. Eighty-three LTC facilities (37.4%) had multiple outbreaks; 37 (16.7%) had three or more outbreaks over the three-year period.
Number of Cases Associated with Outbreaks
Percentage of Cases Associated with Outbreaks
(N = 4,761 Norovirus Events)
Note: Academic years are for the 12 months ended June 30 of each year.
* From facilities determined to have at least one outbreak.
Analysis revealed that norovirus infections comprise 4,761 (41.3%) of gastroenteritis events in LTC facilities in Pennsylvania, with most events occurring during the winter. No substantial decline was evident in norovirus events reported through PA-PSRS in the three most recent norovirus seasons.
This suggests that prevention and control of norovirus gastroenteritis outbreaks continues to be problematic in Pennsylvania LTC facilities.
The symptoms of vomiting and diarrhea are self-limiting and, for most people, resolve within a few days, but these symptoms can be deadly for the older population.4 There is currently no U.S. Food and Drug Administration approved vaccine or cure for norovirus. Recent advances enabling development of human norovirus in the laboratory setting show potential to contribute to vaccine research and targeted treatment methods.8
Authority findings are consistent with CDC data demonstrating that norovirus infections are most common in winter but can occur at any time during the year. According to the CDC, from August 1, 2017, through February 12, 2018, there were 775 norovirus outbreaks reported by nine participating states. During the same period in the previous year, 770 norovirus outbreaks were reported to the CDC by these states. The number of outbreaks reported to the CDC in the 2017-2018 norovirus season to date is above the range reported during the same period over the previous seven years.9
Healthcare facilities may be unprepared to manage large numbers of infected residents. Unchecked norovirus outbreaks can be prolonged, sometimes lasting months. Costs include indirect and direct costs related to staff call-outs, sick leave, and overtime, as well as the costs of additional healthcare cleaning expenses and supplies, such as linens, commodes, bleach, sanitizers, mops, gloves, and gowns. Healthcare facilities may experience financial losses when temporarily closing units or buildings until the outbreak can be controlled or otherwise runs its course.
When new strains of the virus are circulating, norovirus infections can increase by 50%.10
According to 2013 research by Green, "Since 2002, new Gll.4 variants have emerged every 2 to 3 years resulting in epidemics."11 Cannon research shows that "between September 2013 and August 2016 . . . Gll.4 Sydney viruses caused 58% of outbreaks."9 Of the seven main genotypes, four of which infect humans, 49% of the confirmed norovirus outbreaks submitted to CDC from September 1, 2017, through May 31, 2018, were genogroup GII.P16-GII.4 Sydney.12 This comparison of genetic sequencing data with existing sequences contributes to continued efforts to identify trends in norovirus disease outbreaks and preventive measures.13
The best method to control norovirus is to have a preseason plan in place, in which all members of the multidisciplinary team are clear about their roles in prevention, control, and quality improvement measures. The Authority offers a free, online Patient Safety Topic about norovirus. Implemented by a facility's team prior to norovirus season, these tools enable effective preparation, including strategies to prevent widespread outbreak and evaluation of the effectiveness of process and outcome measures. The updated Norovirus Patient Safety Topic includes a concise slide presentation with "train the trainer" notes for staff education.
Pennsylvania Patient Safety Authority Norovirus Preseason Preparedness and Outbreak Control Toolkit
Controlling the Annual Threat of Norovirus Gastroenteritis Outbreaks
Pennsylvania Patient Safety Advisory article presents evidence-based strategies to modify risk factors for outbreaks, including how to prepare for norovirus season, ensure basic outbreak control measures, use enhanced precautions, and conduct leadership and post-outbreak activities.
Norovirus Prevention and Response Recorded Webinar
Designing a Norovirus Prevention and Rapid Response Program: An Evidence-Based Approach.
Norovirus Preparedness Checklist
This sample checklist is designed to help facilities assess facility-specific preparedness plan activities, basic precautions, enhanced precautions, and outcome and process measures.
Acute Gastroenteritis Outbreaks Case Log
Facilities can use this sample log to determine common factors about acute gastroenteritis outbreaks and collect information in a timely, reliable, and organized fashion.
Norovirus Preparedness: Outcome and Process Measures Worksheet
This sample worksheet can be used for documenting facility-specific process and outcome measures associated with norovirus.
Norovirus Preparedness and Control Video
Norovirus preparedness and controlling the annual threat of a norovirus outbreak.
Train the Trainer PowerPoint Slides—NEW!
This short training program for clinicians is accompanied by train-the-trainer notes.
Stop the Spread of Norovirus Poster (for Clinicians)
Norovirus is a highly contagious virus and the principal cause of worldwide acute gastroenteritis epidemics in all age groups. This poster can help ensure healthcare facilities and their staff are better equipped to respond to norovirus.
Stop the Spread of Norovirus Poster (for Patients)
Norovirus is a highly contagious gastrointestinal infection, also referred to as the "stomach flu." This poster can help patients protect themselves.
LTC facilities continue to struggle with annual norovirus outbreaks, despite the existence of accessible state and national resources for prevention and control of this very contagious viral infection. Considering the severe contagiousness and annual onset of norovirus, healthcare facilities are encouraged to implement strategies to help their multidisciplinary teams control initial norovirus cases before they result in an outbreak next season. The Authority encourages LTC facilities to access the Authority Patient Safety Topic on norovirus, which houses all the tools, and select a multidisciplinary team to implement the accompanying strategies to develop a strong preseason prevention and control program.
- Norovirus: U.S. trends and outbreaks. [internet]. Atlanta (GA): Centers for Disease Control and Prevention (CDC); 2015 Dec 10 [accessed 2018 Apr 03]. Available:
- Shah MP, Wikswo ME, Barclay L, Kambhampati A, Shioda K, Parashar UD, Vinjé J, Hall AJ. Near real-time surveillance of U.S. norovirus outbreaks by the Norovirus Sentinel Testing and Tracking Network - United States, August 2009-July 2015. MMWR Morb Mortal Wkly Rep. 2017 Feb 24;66(7):185-9. Also available:
http://dx.doi.org/10.15585/mmwr.mm6607a1. PMID: 28231235
- Lopman B. Norovirus: protecting the vulnerable. [internet]. Medscape.com; 2013 Feb 19 [accessed 2018 Apr 03]. Available:
- Controlling the annual threat of norovirus gastroenteritis outbreaks. Pa Patient Saf Advis. 2010 Dec;7(4):141-8. Also available:
- Stone ND, Ashraf MS, Calder J, Crnich CJ, Crossley K, Drinka PJ, Gould CV, Juthani-Mehta M, Lautenbach E, Loeb M, Maccannell T, Malani PN, Mody L, Mylotte JM, Nicolle LE, Roghmann MC, Schweon SJ, Simor AE, Smith PW, Stevenson KB, Bradley SF, Society for Healthcare Epidemiology Long-Term Care Special Interest Group. Surveillance definitions of infections in long-term care facilities: revisiting the McGeer criteria. Infect Control Hosp Epidemiol. 2012 Oct;33(10):965-77. Also available:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3538836/. PMID: 22961014
- Reporting and surveillance for norovirus. [internet]. Atlanta (GA): Centers for Disease Control and Prevention (CDC); 2016 Dec 28 [accessed 2018 Apr 03]. Available:
- Suspected and confirmed norovirus outbreaks reported by State Health Departments in Massachusetts, Michigan, Minnesota, Ohio, Oregon, South Carolina, Tennessee, Virginia, and Wisconsin to the National Outbreak Reporting System (NORS) by Week of Illness Onset, 2009-2018. [internet]. Atlanta (GA): Centers for Disease Control and Prevention (CDC); 2018 Mar 29 [accessed 2018 Mar 30]. Available:
- Norovirus. [internet]. Philadelphia (PA): Philadelphia Department of Public Health; 2017 Oct 18 [accessed 2018 Apr 03]. Available:
- Cannon JL, Barclay L, Collins NR, Wikswo ME, Castro CJ, Magaña LC, Gregoricus N, Marine RL, Chhabra P, Vinjé J. Genetic and epidemiologic trends of norovirus outbreaks in the United States from 2013 to 2016 demonstrated emergence of novel GII.4 recombinant viruses. J Clin Microbiol. 2017 Jul;55(7):2208-21. Also available:
http://dx.doi.org/10.1128/JCM.00455-17. PMID: 28490488
- Cortes-Penfield NW, Ramani S, Estes MK, Atmar RL. Prospects and challenges in the development of a norovirus vaccine. Clinical Therapeutics. 2017 Aug;39(8):1537-49. Also available:
http://dx.doi.org/10.1016/j.clinthera.2017.07.002. PMID: 28756066
- Cannon JL, Barclay L, Collins NR, Wikswo ME, Castro CJ, Magaña LC, Gregoricus N, Marine RL, Chhabra P, Vinjé J. Genetic and epidemiologic trends of norovirus outbreaks in the United States from 2013 to 2016 demonstrated emergence of novel GII.4 recombinant viruses. J Clin Microbiol. 2017 Jul;55(7):2208-21. Citing: Green KY. 2013. Caliciviridae: the noroviruses, p 586-608. In Knipe DM, Howley PM, Cohen JI, Griffin DE, Lamb RA, Martin MA, Rancaniello VR, Roizman B (ed), Fields virology, 6th ed. Lippincott Williams & Wilkins, Philadelphia, PA.
- CaliciNet Data: genotype distribution of norovirus outbreaks September 1, 2017 - February 28, 2018. [internet]. Atlanta (GA): Centers for Disease Control and Prevention (CDC); 2018 Mar 6 [accessed 2018 Jun 11]. Available:
- Norovirus reporting in CaliciNet. [internet]. Atlanta (GA): Centers for Disease Control and Prevention (CDC); 2014 May 12 [accessed 2018 Mar 30]. Available: